This proposal concerns studies on the genetics and structure- function relationships of bacterial ribosomes. A. Are there several ribosomal modifying enzymes located near minute 0 on the E. coli chromosome? The 16 RNA methylase which determines responsiveness of the 30S subunit to kasugamycin has already been described. Studies are now being done to determine whether the chromatographic alteration of protein S4 due to a mutation which maps near ksgA is due to another modifying enzyme. B. Studies on the molecular biology of erythromycin dependence in E. coli. Altered binding of erythromycin to 50S subunits from erythromycin dependent mutants has been observed; the structural alteration responsible for this behavior has not yet been defined. C. Other studies will concentrate on ribosomes from N. gonorrhoeae. We have defined a cluster of genes which probably affects the gonococcal ribosome. Two of these genes determine resistance to streptomycin and spectinomycin due to alteration of 30S subunit. Several other nearby genes may also alter the ribosome of this organism; ribosomes from these mutants will be studied in a cell free protein synthesizing system and their structural proteins will be compared by gel electrophoresis and column chromatography.